High energy fuels containing ethylene imine



Unite States HIGH ENERGY FUELS CONTAINING N Drawing. Appiicationslune 22, 1951 Serial N 0. 233,108

Claims. (Cl. 52-.5)

This invention'relatesito fuels, to methods of producing them, and to methods of utilizing .them; and'includes fuelscapable ofuse in conventional internal combustion engines bothof the spark-ignitedand diesel types, but more particularly is concerned with fuels for jet propulsion, .as'for example in rockets.

The need .for fuelsof characteristics suitable for jet propulsion has been widely high-lighted in recent years. While many fuel compositions have been suggested for suchpurposes, the exacting requirements in this art emphasize the fact that the demands have notbeen met. Some of the important characteristics in this connection are a high energy fuel that maybe easily handled without undue hazard, of relatively high density, high boiling point, low freezing point, high heat of formation, and exhibiting spontaneous combustibility in the presence of a specified amount of a hypergolic oxidant. (The term 'hypergolic is used in its ordinary meaning of spontaneouslycombustible; so that a hypergolic oxidant is one which in contact with a given fuel in proper proportions produces spontaneous combustion.) The stated properties of fuels as given above are not all consistent with one another so'that a balance or compromise must be made. This has led to fuels which because of such compromise are not as satisfactory as they should be.

Among the objects of the present invention is the production of fuels of wellbalanced properties for use in jet propulsion.

Further objects include conventional fuels with additives which convert them into super fuels for jet propulsion use.

Still further objects include conventional fuels with additives which materially improve their characteristics for conventional use.

Still further objects include methods of utilizing such fuels.

Still further objects and advantages of the present invention will appear from the more detailed description set forth below,.it being .uuderstoodthat such more detailed description is given by way .ofillustration and explanation only, and not by way of limitation, since various changes therein may be made by those skilled in the art without departing from the scope and spirit of the present invention.

in accordance with the present invention, fuels of novel type having unique properties are produced by utilization of ethylene imine as a component of such fuels. Ethylene imine has the formula NH Cz Generally these fuels may be designated as compositions containing ethylenelimine alone or an lgnitible organic liquid with an. amount of ethylene imine added thereto burn-out of'the engine or any of its parts.

, 2,824,791 Patented Feb. 25, 1958 ice =3 useful properties as fuels for jet propulsion purposes, and, in fact, for these purposes, they are superior to the ignitible'liquids alone. The liquids referred toinelude materials which are conventionally used at present as fuels, or are being developed experimentally for fuel ,a higher theoretical,specificimpulsewhen used ,as a jet propulsion fuel, than do most of the commonly used fuels. The specific impulse is a measure of the energy deliverable by the fuel and a higher specific impulse makes possible an increased range or trajectory of a vehicle driven by jet propulsion, or an increased payload, or a decreased fuel consumption.

Consequently, the addition of ethylene imine to an ignitible'liquid whose theoretical specific impulse is less than that of ethylene imine results in a mixture Whose theoreticalsspecific impulse lies between that of the ignitible liquid alone and that of'ethylene imine, resulting thereby in an increase in the theoretical. specific impulse .of the ignitible liquid, the extent of the increase depending on, and in general, being in proportion to (not necessarily linearproportion) the amount of ethylene imine contained.

When employing these mixtures as fuels any oxidizing substance in use for thecombustion of fuels for jet propulsion may be used. For example, air, gaseous ox gen,

liquid oxygen, nitric acid, mixed acid, hydrogen peroxide,

7 or nitrogen tetroxide.

Although a maximum increase in specific impulse is produced by using a maximum quantity of ethylene imine,

other practical considerations connected with the particular applications of the fuels often lead to preferred mixtures containing less than the maximum quantity of ethyl ene imine. The most important considerations are customarily cost, availability and physical properties. These considerations are balanced one against the other, and the most desirable compromise of useful characteristics .chosen. 'The requirements depend on the specific application: For example, in some cases a freezing point of the fuel of 0 C. or lower is satisfactory, but in other cases-a'freezingpoint of .40 C. or lower is necessary. Differences in physical properties of this type are attainable by varying the relative proportions of ethylene imine in the fuels. Sometimes, in order to achieve an ideal balance of desired properties, it is preferable to use combinations of more than one ignitible-liquid in addition to the ethylene imine.

Furthermore, in order to achieve a desirable balance of excellent physical properties while maintaining a comparativelyhigh theoretical specific impulse, it is often found advisable to add certain components to the ethylene imine, which added components mayor may not be ignitible. Forexample, water in quantities of 0.1% to '25% by weight may be added to ethylene imine or any of the compositions containing ethylene imine, in order to lower the temperature of the combustion gases and These properties are desirable in connection with preventing The increased heat capacity imparted by the addition of water is very useful for regenerative cooling of rocket engines. Thus water may be included in ammonia-ethyleneimine fuels. As much as 65-66% water may be-added'to-ethylene actual use.

iminewhile retaining hypergolic properties. In similar fashion, hydrazine or ammonia may be added to ethylene imine in quantities ranging from 0.1% to 99% by Weight, since they also lower the combustion temperature and increase the heat capacity of ,thefuel. These substances can be added in greater quantity than water, because they alsohave high theoretical specific impulses and will not lower that of ethylene imine appreciably.

It is notable that the superior properties ethylene imine when added to other ignitible liquids consist not only in an increase of the theoretical specific impulse, but also in improved ignition andcombustion characteristics.

Outstanding in this'respect is its ability to render other ignitible liquids spontaneously inflammable when brought into contact with'certain oxidizing agents,

specifically; nitric, acid, nitric acid containing nitrogen tetroxide '(red fuming nitric acid) and mixed acid (nitric acid plus sulfuric acid). It also has the ability to improve this property in ignitible liquids which already possess the property to some degree.

' aliphatic, aromatic and heterocyclic amines such as isoa parted by 7 This property of spontaneous inflammability on contact with an oxidizer may be termed hypergolic ignitibility. It is a very. desirable property for many applications in rocket propulsion, since it eliminates the requirement of an external source of ignition, resulting in reduced weight.

and greater simplicity in design and constructionof the vehicle; furthermore, in many cases it produces safer starting characteristics and smoother combustion.

and mixed acid, with which these ethylene imine-containing compositions are hypergolic, are commonly used as rocket propellants, and may be referred to as rocket propellant oxidizers. 1

If it is desired to imparthypergolic properties to a fuel, or to improve the already existing hypergolic properties of a fuel, an'amou'nt of ethylene imine may be added which accomplishes the desired objective with the particular oxidizer employed and under the conditions of on the nature of the fuel, the nature and c'oncentration'of the oxidizer, and the conditions under which it is used- The quantity, required depends for example lene; alcohols such as methanol, ethanol, alcohol;

propyl-amine, diethylamine, triethylamine, aniline, cyclohexylamine, pyridin; compounds of nitrogen and hydro-' gen including ammonia, hydrazine and, hydrazines in which hydrogen has been replaced by organic substituents; methylal; jdiethylether; cyclic oxidessuch as ethylene oxide, propylene oxide, dioxane, furanje, andtetrahydrofurane; mercaptans such as mixedbutyl mercaptans, ter tiary-butyl-mercaptanyetc.g r 1 Any or all of. these liquids mayither'e'fore be used with ethylene imine as an additive to 'improve the theoretical. specific impulse, and the range of concentrations of ethylene imine which may be used varies between 0.1% and 99% by weight ethylene imine.

However, the usefulness of ethylene imine as an addi-' tive is not limited to the materials listed above, since these' materials represent classes of compounds, of which any individual member may be used effectively for the same purposes; and similar desirable fuel characteristics are imparted to them by. the addition'of ethylene imine.

' Therefore, ethylene imine is correspondingly" effective with other aliphatic including saturated and olefinic, aro- .matic and -hydroaromatic hydrocarbons, .or mixtures oxidizers, white fuming'nitric acid, red fuming nitric acid indicated. a

thereof, such as JP-l or JP-3; also with alcoholsjalkyl,

aromatic, hydroaromatic and heterocyclic amines; ethers and heterocyclic, oxides; mercaptans; also combinations .of these ,classesso that binary, ternary and higher mixtures may be used. i r

The following examples illustrate the inventiomparts or ratios or. percentages being by weight unless otherwise Ethylene imine was found to be'miscible in all proportions in gasoline and a solution containing 16.5% by- 'weight of ethylene imine showed no separation of solid or liquid phase when cooled to (3., A solution of the same concentrationignited spontaneously when a few drops of it were added directly to 0.5;mls. of 9 6% nitric .acid. Gasoline alone does not ignite spontaneously with ;Compositions containing higher amounts than the hyspark, powder squib); that is, ignition is more positive and I ignition delay is decreased. concomitantly, smoother combustion is also attained. The specific amounts pre- 'ferred for this purpose depend on the fuel, the oxidizer, the strength of oxidizer, the type of igniter, and the conditions of use. be improved, by adding a maximum amountof ethylene Jimine, the amount used may be greater, depending on all practical'considerations balanced against each other.

Ithas been found that ethylene imine is miscible in all proportions with the ignitible liquids listed below, and

we have also found that the solution resulting where ethylene imine is added to any one of these liquids'has a higher theoretical specific impulse when burned with an oxidizer in anytype of jet propulsion device than has the liquid to which no ethylene imine has been added.

The extent of increase in specific impulse resulting from the addition of ethylene imine varies with the amount of the'latter that is added, and is, in general, in proportion (not necessarily linear proportion) to the amount added.

However, since the'specific impulse can The ignitible liquids referred to above are: hydrocarbons including gasoline, N-hexane, kerosene, petroleum ether. (boiling range '3 0-60 Q), cnzene, toluene, xy-

nitric acid unde'r'these conditions.

pergolic amount referred to above may be 'used, for example ethylene gasoline imine HMO! .FP

mane

new

zewuzz Compositions containing amounts of ethylene imine less than hypergolic are illustrated by: a

ethylene gasoline imine A solution of n-hexane containing 23.9% weight of ethylene imine ignited spontaneously when'brought into contact with 96% nitric acid. .N-hexane alone .does not ignite spontaneously with nitric acid under these condi Compositions containing lesser amounts of ethylene 1mine,are'for example i eth lene n-hexane is... 5

Ethylene imine was found to be miscible in all proportions in liquid ammonia. A solution containing 50% ethylene imine by weight ignited spontaneously when contacted with 85 nitric acid.

Compositions containing higher or lower amounts of ethylene imine may be used depending on the purposes in hand.

Ethylene imine was found to be miscible in all proportions in aniline, and a solution containing 22% by weight of ethylene imine had a freezing point of approximately -40 C. This mixture showed hypergolic ignition with 95% nitric acid.

Other compositions include for example: 10% ethylene imine with 90% aniline; and 20.5% ethylene imine with 79.5% aniline. Illustrative ternary compositions are:

ethylene aniline hydrazine mime Ethylene imine is miscible in all proportions with ethyl alcohol. A solution containing by weight of ethylene imine is hypergolic with 95% nitric acid. Other alcohol compositions may be:

alcohol ethyleie 5 5 VII VIII

Ethylene imine was found to be miscible in all proportions with diethylamine, and a solution containing 20% by weight of ethylene imine ignited spontaneously on contact with 95 nitric acid. Compositions contain- 6 ing higher or lower amounts of ethylene imine may be used depending on the purposes in hand.

Ethylene imine was found to'be miscible in all proportions with isopropylamine, and a solution containing 30% by weight of ethylene imine ignited spontaneously on contact with 95% nitric acid. Compositions containing higher orlower amounts of ethyleneimine maybe used depending on the purposes in hand.

Ethylene imine was found to be miscible in all proportions with toluene, and a solution containing 40% by weight of ethylene imine ignited spontaneously on contact with 95% nitric acid. Compositions containing higher or lower amounts of ethylene imine may be used depending on the purposes in hand.

A solution containing 30% by weight of ethylene imine in toluene ignited spontaneously on contact with mixed acid. The mixed acid was composed of 82% nitric acid, 15% sulfuric acid and 3% water. Compositions containing higher or lower amounts of ethylene imine may be used depending on the purposes in hand.

XII

Ethylene imine was found to be miscible in all proportions with a solution of mixed butyl mercaptans. A mixture containing 30% ethylene imine ignited spontaneously on contact with 85% nitric acid. Compositions containing higher or lower amounts of ethylene imine may be used depending on the purposes in hand.

XIII

Ethylene imine was found to be miscible in all proportions with tetrahydrofuran. A solution containing 30% by weight of ethylene imine ignited spontaneously on contact with nitric acid. Compositions containing higher or lower amounts of ethylene imine may be used depending on the purposes in hand.

In the ternary fixture of ethylene imine with hydrazine and aniline, the imine may be used advantageously for example, to lower the freezing point of the system to below -40 C. Thus 12.8% hydrazine, 78.6% aniline, and 8.6% ethylene imine (all by weight) has a freezing point of 43 C. Appreciable amounts of water may be present without raising the freezing point above 40" C. which may be taken as a generally desirable freezing point limitation on jet propulsion fuels. Thus a ternary composition freezing at 42 C. with 2% water added showed a freezing point of 4l.0 C. 5% of water was required to raise the freezing point to 39.2 C. So that if a 95% grade hydrazine (containing 5% water) is used in preparing the ternary mixture, it would contain only 0.6% water. Consequently the solution will have a freezing point below -40 C. even if considerable contamination with water has occurred. Ethylene imine may be added to the eutectic of 17.3% hydrazine and 82.7% aniline or other mixtures thereof to improve the ignition characeristics very materially.

Having thus set forth our invention, we claim:

1. A fuel composition of matter consisting essentially of gasoline and ethylene imine in an amount to give the composition hypergolic properties.

2. As a motor fuel, gasoline and ethylene imine, the latter being 16.5% by weight of the fuel.

3. As a motor fuel, gasoline and ethylene imine, the latter being 53.2% by weight of the fuel.

4. As a motor fuel, gasoline and ethylene imine, the latter being 27.6% by weight of the fuel.

5. As a motor fuel, gasoline and ethylene imine, the latter being 17.8% by weight of the fuel.

(References on following page) 

1. A FUEL COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF GASOLINE AND ETHYLENE IMINE IN AN AMOUNT TO GIVE THE COMPOSITION HYPERGOLIC PROPERTIES. 